Hi, I’m curious if this can be rewritten with `when` block (`hasMaxRole` is extension method on my `...

# announcements

[bmarinovic]

Hi, I’m curious if this can be rewritten with when block (hasMaxRole is extension method on my User data class):

if (loggedInUser.hasMaxRole(<http://Role.NO|Role.NO>_ROLE)) {
    ResponseEntity(HttpStatus.FORBIDDEN)
} else if (loggedInUser.hasMaxRole(Role.USER_ROLE)) {
    if (loggedInUser.id == id) {
        ResponseEntity.ok(loggedInUser)
    } else {
        ResponseEntity(HttpStatus.FORBIDDEN)
    }
} else {
    userApiService.findById(id)
}

I would like something like this:

when(loggedInUser) {
    hasMaxRole(<http://Role.NO|Role.NO>_ROLE) -> ResponseEntity(HttpStatus.FORBIDDEN)
    hasMaxRole(Role.USER_ROLE) && (loggedInUser.id == id) -> ResponseEntity.ok(loggedInUser as Any)
    hasMaxRole(Role.USER_ROLE) ->  ResponseEntity(HttpStatus.FORBIDDEN)
    else -> userApiService.findById(id)
}

(even with this code, I am repeating loggedInUser in second match since I need to call it twice in && operation)

[Jakub Pi]

The easiest way is to rewrite your extension function to return the actual Role, and then branch based on that. Remember you can use the in operator to check for whether a value belongs to a collection. Assuming Role is an enum or a sealed class, the compiler will check whether you've considered all branches.

[Jakub Pi]

when(loggedInUser.role) {
  NO_ROLE -> ResponseEntity(HttpStatus.FORBIDDEN)
  USER_ROLE -> if(id == loggedInUser.id) ResponseEntity.ok(loggedInUser) else ResponseEntity(HttpStatus.FORBIDDEN)
  in OTHER_ROLES -> ...
  else -> userApiService.findById(id)
}

[bmarinovic]

Well, the User has List<Role> so that complicates things

[bmarinovic]

that’s why I tried to call “calculating” method in each branch

[Jakub Pi]

Yeah that's why I gave an example of using in.. You can create a static list on the companion object to store the set of validated roles to check membership

[bmarinovic]

ok, thanks 🙂

[Jakub Pi]

One other thing you can do is create an extension function that is just a predicate.. it should basically check it and role and return true if both match. That way you can roll the two cases together.

[Jakub Pi]

fun User.canLogin(id : String) : Boolean = id == this.id && this.hasMaxRole(Role.USER_ROLE)

[Jakub Pi]

This would be the alternative if you want to use when {} without an object.

[Jakub Pi]

when {
  loggedInUser.canLogin(loggedInUser.id) -> ...
  loggedInUser.role in EnumSet.of(NO_ROLE, USER_ROLE) -> ...
  else -> ...
}

[bmarinovic]

thanks for the solutionS 🙂 I’ll choose something which seems best to me